Magnetic separator and cooling system



Oct. 26, 1954 K. A. BLIND 2,692,673

MAGNETIC SEPARATOR AND COOLING SYSTEM Filed Dec. 17, 1951 I 5 Sheets-Sheet l wwz/vra/e BY 16a. 6

AITUE/VE P15 Oct. 26, 1954 K. A. BLIND 2,692,678

MAGNETIC SEPARATOR AND COOLING SYSTEM Filed Dec. 1'7, 1951 5 Sheets-Sheet 2 Oct. 26 1954 BUND 2,692,678

MAGNETIC SEPARATOR AND COOLING SYSTEM Filed Dec. 17, 1951 5 Sheets-Sheet 3 INVENTOR.

t y Q'eflm/iflim/ Oct. 26, 1954 K. A. BLIND MAGNETIC SEPARATOR AND COOLING SYSTEM 5 Sheets-Sheet 4 Filed Dec. 17 1851 Oct. 26, 1954 K. A. BLIND 2,692,678

MAGNETIC SEPARATOR AND COOLING SYSTEM Filed Dec. 17, 1951 5 Sheets-Sheet 5 Patented Oct. 26, 1954 MAGNETIC SEPABATOR AND COOLING SYSTEM Karl A. Blind, Thiensville, Wis., assignor to Dings Magnetic Separator 00., Milwaukee, Wis., a corporation of Wisconsin Application December 1'7, 1951, Serial No. 262,011

10 Claims. 1

The present invention relates generally to improvements in the art of separating magnetic material from mixtures of .magnetic and nonmagnetic particles, and relates more specifically to improvements in the construction and operation of electrically energized magnetic separators of the endless carrier type.

The primary object of this invention is to provide an improved separator embodying lectrically energized magnets, which i simple and compact in construction and highly efli'cient in operation.

It has heretofore been common practice to utilize an endless carrier such as a belt or drum of non-magnetic material cooperating with one or more electrically energized magnets, for the purpose of separating magnetic particles from mixtures of the latter with non-magnetic substances, by subjecting the bulk mixture to a field of magnetic influence created by the magnets and which is sometimes submerged in liquid and extends along a surface of the advancing carrier. The direct current electro-magnets employed in this type of separating unit must embody sufiicient iron to maintain proper saturation of the separating field at all portions of the flux path, but the magnetomotive force derived from the ampere turns in these energizing coils is however limited by the space between the successive poles of the magnets; and it is well known that any increase in the transverse cross-section of the magnet poles not only reduces the available space for ampere turns, but also increases the interpolar leakage.

Although the energizing coils of the magnets of some of these eparators have heretofore been superficially cooled by immersing them in a bath of oil and by subjecting the pole faces to liquid in the separating zone, this prior practice did not materially improve the efficiency of these units. I have discovered that by specially constructing the pole cores so as to locally increase the transverse cross-sections while reducing the lengths thereof, by also specially constructing the magnet energizing coils so as to materially reduce the amount of copper therein, and by introducing forced circulation of cooling liquid about these coils, the field intensity within the separating region can be vastly increased and excessive heating due to necessarily greater power consumption as well as abnormal leakage losses can be effectively eliminated. I have also found that by utilizing strip wound energizing coils directly exposed to rapidly circulating cooling 2 oil or the like, the heat transfer is augmented and a scrubbing action tending to keep the transfer coil surfaces clean results, and the cooling effect may also be improved by delivering the cooling liquid to the coil confining space through hollow current conductors.

It is therefore an important object of the present invention to provide an improved direct current magnet assembly especially applicable to magnetic separators for mixed magnetic and non-magnetic materials, and which will economically insure maximum percentage of separation of the materials.

Another important object of my invention is to provide an improved liquid cooled electromagnet of the direct current type, which is exceedingly compact but powerful for use in creating a local magnetic separating field of high intensity.

A further important object of this invention is to provide an improved high intensity magnet assemblage and cooling system therefor, in which the heat is most effectively dissipated from the energizing coils.

Still another important object of my present invention is to provide an improved magnetic separator in which the actuating magnets are energized by direct current and wherein successive magnets may be compactly grouped and confined within a small enclosure without introducing excessive interpolar leakage losses.

An additional important object of the invention is to provide an improved endless carrier type of magnetic separator having direct current high intensity electro-magnets and wherein overheating and leakage losses are minimized.

A further important object of this invention is to provide an improved magnetic separator especially adapted for the treatment of granular material immersed in liquid, and wherein most effective cooling of the magnets is assured at all times so as to insure maximum separating efficiency with minimum power consumption.

These and other objects and advantages of my invention will be apparent from the following description from which it will also be noted that the gist of the improvement is the provision of a magnetic separator having an endless carrier for the materials under treatment, one advancing face of which has a field of magnetic influence extending therealong and created by powerful electro-magnets coacting with the opposite face of the carrier, and wherein relatively small magnet poles are energized by compact direct current coils constantly subjected to rapid cooling and cleansing action by forced rapid circulation of liquid thereabout.

A clear conception of the several features constituting my present invention, and of the mode of constructing and operating magnetic separators embodying the same, may be had by referring to the drawings accompanying and forming a part of this specification in which like reference characters designate the same or similar parts in the various views.

Fig. l is a side elevation of an endless belt type of wet magnetic separator showing the circulating mechanism for the magnet coil cooling liquid;

Fig. 2 is a longitudinal vertical section through the \vet magnetic separator of Fig. 1, showing the general assemblage of the electro-magnets and the separating zone associated therewith;

Fig. 3 is a top-view of the wet magnetic separator of Figs. 1 and 2, but with the upper run of the conveyor belt broken away so as to more clearly reveal the multiple magnets of the unit;

Fig. 4 is an enlarged part sectional top view of one of the direct current electro-magnets of the separator shown in Figs. 1 to 3 inclusive;

Fig. 5 is a similarly enlarged part sectional end view of the eleetro-magnet of Fig. 4;

Fig. 6 is a likewise enlarged part sectional side view of the electro-magnet shown in Figs. 4 and 5;

Fig. 7 is a fragment of one of the crossover connections between the strip coils of one of the energizing magnets;

Fig. 8 is a longitudinal central horizontal section through a drum type of wet magnetic separator also embodying the invention; and

Fig. 9 is a transverse vertical section through the drum type separator of Fig. 8.

While the invention has been shown and described herein as being advantageously applicable to wet-magnetic separators of the type having endless carriers consisting either of an endless belt or of a revolving drum and wherein several successive electro-magnets are utilized to create the separating field of magnetic influence, it is not the intent to unnecessarily restrict the utility of the improved features by virtue of this limited showing; and it is also contemplated that specific descriptive terms used herein be given the broadest possible interpretation conseparator shown therein, comprises in general, V

a constantly advancing endless carrier or belt ll of non-magnetic substance, coacting with upper and lower driving and idler pulleys l2, l3 respectively, rotatable about parallel horizontal axes; an elongated succession of electro-magnets l4 confined within a closed casing l5 and each having direct current energizing coils l5 and a core I! provided with a pole shoe l8 disposed closely adjacent to the upper surface of the bottom run !9 of the belt ii; a mixed materia1 supply launder 26 and feed tray 2| for supplying a granular mixture of magnetic and non-magnetic particles suspended in liquid, to the lower surface of the advancing belt run l9 near the pulley iii; a non-magnetic particle or tailings receiving hopper 22 forming a liquid basin 2% at the delivery end of the feed tray 2i and in which the mid-portion of the belt run I9 is normally submerged; a stationary magnetic material guiding and pickup plate 24 extending upwardly from within the basin 22 and communicating with a magnetic particle or concentrate discharge bin 25; and devices including a pump 26 and a heat exchanger 21' for continuously circulating cooling liquid through the magnet housing casing 5.

The various elements of the magnetic separator and of the magnet cooling system are all mounted upon a sturdy main frame 29 as shown in Fig. 3, and the endless carrier belt I I may be formed of any suitable nonmagnetic material and has a relatively heavy belt tensioning and contact roller 30 cooperable with its upper stretch or run in order to cause the lower belt run I9 to travel along and in snug engagement with the curved bottom plate of the magnet confining casing [5. The pulleys I2, l3 are journalled in suitable bearings carried by the main frame 29, and the endless belt normally travels in the direction indicated by the arrows in Figs. 1 and 2 and may be driven by power applied to the upper pulley 42. The separating region or zone extends along the bottom face of the lower stretch [9 of the belt I I within the liquid of the basin 23 as depicted in Fig. 2.

The group or bank of direct current magnets 14 is fixedly suspended from the main frame 29 between the pulleys I2, l3 and between the upper and lower stretches of the belt H, by means of cross-beams 3| secured to top plates 32 which carry the individual magnets and form a cover for the magnet confining casing l5, and the successive magnets are of opposite polarity in order to cause the magnetic particles which are carried through the separating zone by the belt H, to be constantly agitated so as to release any confined non-magnetic particles. Each of the individual magnets It has its core I! secured to the adjacent top plate 32 by means of one or more studs 33, and in order to permit the successive magnets to be placed as close to each other as possible and to create a uniformly distributed magnetic field of maximum intensity at the separating zone which extends along the lower face of the belt run IS), the initial magnets 14 of the series are specially constructed as illustrated in detail in Figs. 4 to '7 inclusive.

From Figs. 4 to 7 inclusive it will be noted that the cores I! of the high intensity direct current magnets are of composite construction each comprising an upper section 35 of relatively large transverse cross-sectional area, and a lower section 36 of considerably smaller transverse crosssectional area firmly secured to the adjacent upper section 35. The upper larger core section 35 is surrounded by a series of flat strip wound copper coils 31, while the lower smaller core section 35 is embraced by a similar series of fiat strip wound copper coils 38, but due to the difference in cross-sectional area of the core sections 35, 36, the number of ampere turns in the lower coils 38 is more than that in the upper coils 3'! so that maximum field intensity will result at the pole shoes 3 which are secured as by welding to the lower extremities of the cores [1. The successive coils 3'1, 32 of each series are interconnected by bridge or jumper plates as shown in Fig. '7,

and are separated from each other by spacers 4| and from the cores H by mica sheets 32 as indicated in Fig. 6, and the successive magnets are arranged in laterally adjacent pairs as depicted in Fig. 3 and are all spaced apart sufiiciently to permit free circulation of cooling liquid such as oil about and in direct contact with the coil sections 31, 38 thereof.

The launder or supply trough 20 may also be secured to the main frame 22 of the separating unit and should be maintained filled with sufficient mixture of water and mixed magnetic and non-magnetic granular material to cause the latter to constantly flow into the space between the lower belt run l9 and the inclined feed tray 2| as shown in Fig. 2. The hopper 22 with which the lower end of the feed tray 2| communicates beneath the surface of the liquid basin 23, has a bottom discharge opening 44 for the delivery of separated non-magnetic particles or tailings, and is also provided with an overflow 45 for excess liquid and which maintains the separating zone properly submerged. The inclined magnetic particle pick-up plate 24 which has its lower end immersed in the basin 23, extends upwardly slightly beyond the last magnet l4 of the series and is provided with a chute 46 for directing the magnetic particles or concentrates into the bin 25, and this bin has a final concentrates discharge spout 41 at its bottom.

In order to enable the magnets I4 to be properly energized so as to produce a magnetic field of high intensity within the separating zone beneath the belt run l9, while preventing overheating of these magnets, they should be constantly and effectively cooled. This is accomplished by confining the magnets |4 within the sealed casing l5 and by continuously circulating cool liquid such as oil in abundant quantities, about the magnet coils 6 with the aid of the pump 26. The pump 26 is motor driven and has its inlet conduit 49 connected to a sump 50 while its discharge conduit 5| communicates with the inlet end of a heat exchanger 2'! of any type adapted to cool the oil flowing therethrough. The opposite outlet end of the heat exchanger 21 communicates through a pipe 52 with one end of the magnet confining casing |5, the opposite end of which is connected to the sump 5|] by a pipe 53, as shown in Figs. 1 and 3. The pump 26, heat exchanger 2'! and sump 50 are all of standard and well known construction readily available on the market and the conduits 49, 5| and pipes 52, 53 should be provided with pipe unions 54 in order to facilitate installation.

When the various parts of the magnetic separator shown in Figs. 1 to 7 inclusive have been properly constructed and assembled, the normal operation of the unit is as follows. The endless carrier belt I will normallly be driven by power applied to the upper pulley |2 to cause the lower curved run |9 thereof to constantly advance through the separating zone within the liquid basin 23 from the feed toward the discharge end of the separator, and in contact with the bottom of the casing l5. The direct current magnets |4 should be energized to produce a magnetic field of high intensity within and extending throughout the entire length of the separating zone, and the cooling oil circulating pump should also be operated to cause cool oil under pressure to constantly flow through the casing |5 in contact with all external portions of the magnet coils |6 as indicated by the arrows in Fig. 3.

With the unit operating in this manner, liquid containing mixed magnetic and non-magnetic particles in suspension may be admitted in abundance from the feed launder and along the inclined feed trough 2| to separating zone wherein the major portion of the magnetic particles will promptly be attracted toward the under side of the belt run I 9 by magnetic influence and will be held against the belt, while most of the nonmagnetic particles will drop into the hopper 22 and will descend through the liquid in th basin 23 upon reaching the lower end of the feed tray 2|. The magnetic particles which cling to and advance with the belt run I9 will be subjected to magnetic flux of opposite polarity as it passes the successive magnet pole shoes l8, thereby causing the magnetic particles to roll back and forth so as to free entrained non-magnetic particles and to permit the latter to drop into the tailings hopper 22; and the final concentrates or magnetic particles are ultimately delivered upon the discharge chute 46 and into the bin 25 when they are carried beyond the separating zone, while excess liquid flows over the overflow wier 45. The tailings may be constantly withdrawn from the hopper 22 through the opening 44, while the concentrates may be likewise withdrawn through the bin outlet spout 47, thus permitting separation to be carried on continuously.

While the invention is shown in Figs. 1 to 7 inclusive as being advantageously applicable to the Well known endless belt type of magnetic separator, it is also applicable to other types as for instance the drum type shown in Figs. 8 and 9. This drum type of separator comprises in general a constantly revolvable rigid drum 6| having opposite end heads 62 journalled for rotation upon a fixed central shaft 63; a series of magnets 64 confined within the lower portion of the drum 6| the upper interior of which is divided into two parts by a stationary partition 65, and each magnet 64 having direct current energizing coils 66 and a core 61 provided with a pole shoe 68 disposed closely adjacent to the upper internal surface of the lower peripheral portion 69 of the drum 6| a mixed material supply launder 70 and feed tray H for supplying a mixture of granular magnetic and non-magnetic particles suspended in liquid to the lower outer surface of the drum portion 69; a tailings receiving hopper 12 forming a liquid basin 13 at the delivery end of the feed tray H and in which the lower drum portion 69 is constantly submerged; a stationary guiding and pick-up plate 14 for magnetic material extending from within the basin 13 to a point beyond the magnets 64 and communicating with a concentrate discharge chute l5; and means including central conduits l6, 7'! formed in the shaft 63 and communicating with the interior of the drum 6| on opposite sides of the fixed partition 65 through openings l8, respectively, for effecting a continuous circulation of cooling liquid about the magnet coils 66.

The various elements of this drum type separator may be mounted upon a sturdy main frame and the annular drum 6| may be formed of any suitable non-magnetic material while the end heads 62 are formed of durable metal of any kind and are journalled in anti-friction bearings 8| mounted upon cylindrical end portions of the fixed shaft 63. The drum 6| is adapted to be rotated in the direction of the arrow shown in Fig. 9, by power applied to a sprocket 82 secured to one of the end heads 62, and the medial portion of the shaft 63 to which the partition 65 is secured may have enlarged polygonal crosssection in order to enhance its rigidity. The separating region or zone of this drum type unit extends along the exterior of the curved bottom face of the advancing lowerdrum portion 69 well beneath the level of the liquid within the basin 73, as illustrated in Fig. 9.

The direct current magnets 64 of the drum separator may be constructed substantially the same as those of the belt type separator previously described, with flat strip wound copper coils 6'6 coacting with composite cores 61. The successive magnets 64 are also of reversed polarity and all of the magnets 64 are secured to sturdy top plates 84 by means of studs 85, and the plates 84 may be suspended from the medial polygonal portion of the stationary shaft 63 by similar studs. The magnets 64 are also adapted to create a magnetic field of high intensity within and along the separating zone, and are spaced apart sufficiently to permit free flow of cooling oil which substantially fills the drum 6| about and in direct contact with the outer extensive surfaces of the coils 66.

In order to effect proper circulation of the cooling liquid about the magnet coils 66, a pump 26, sump 5c and heat exchanger 21 such as shown in Figs. 1 and 3, may be utilized. The pump connections will be the same as previously described, but the cool oil supply pipe 52 should be caused to communicate with one of the conduits i6, 11 in the shaft 63 while the oil return pipe 53 should be connected to the other central shaft conduit. With the circulating system thus installed, the pump 26 will produce a constant and rapid circulation of cooling liquid under pressure through the conduits 16, TI and openings l8, l9 and through the spaces on the opposite sides of the partition 65 and in intimate contact with the coils 66 of the magnets 84, and the liquid will be continuously cooled in the heat transfer device or heat exchanger 21.

During normal operation of the drum type separator shown in Figs. 8 and 9, the endless carrier or drum 5! will be constantly revolved by power applied to the sprocket 2, to continuously advance the lower arcuate peripheral drum portion 59 along the separating zone and through the liquid in the basin i3 as indicated by the arrow in Fig. 9. The direct current magnets 54 should be energized to produce the high intensity magnetic field within the separating zone and extending along the drum periphery from the tray H to the chute 15, and cooling oil should be continuously circulated by the pump through the conduits 16, Ti and openings 18, 19 and through the interior of the drum 6| about the magnet coils 66 as indicated by the arrows in Fig. 9.

While the unit is operating in this manner, liquid containing mixed magnetic and non-magnetic particles may be admitted to the launder T and delivered in abundant quantities upon the upper end of the feed tray II from whence it flows along and in contact with the advancing lower outer surface of the drum portion 69. As the admitted liquid and granular material enters the magnetic separating zone, the magnetic particles are promptly withdrawn from the mixture and cling to the advancing peripheral drum portion 69 under the influence of the high intensity magnetic flux, while the major portion of the non-magnetic particles advance along and drop over the lower end of the tray H and ultimately descend through the basin 13 into the tailings hopper 72. The advancing magnetic particles which adhere to the drum 6| are rolled about so as to release entrained non-magnetic particles, and the relatively pure concentrates H are eventually delivered from the basin l3 past the pick-up plate 14 and onto the chute i beyond the end of the magnetic field.

Both of the illustrated types of magnetic separators function in substantially the same man- 8. ner and most eifective separation or removal of the magnetic concentrates from the non-magnetic tailings is assured by the improved construction of the magnets and by the mode of preventing excessive heating thereof. The formation of at least the medial magnetic of each series with cores having sections of greatest transverse area remote from the separating zone and with windings or coils having more ampere turns nearest this zone, enables the successive magnets to be placed closely adjacent to each other while still providing ample space for forced circulation of cooling liquid about the coils. The flat strip winding of the magnetic energizing coils provides extensive surfaces for the transfer of heat from the coils to the cooling liquid, and also causes the liquid to create a scouring or cleansing action along the contacted coil surfaces; and the rapid forced circulation of cool liquid about these coils positively eliminates excessive heating even when high voltage is applied.

From the foregoing detailed description it will be apparent that the invention in fact provides an improved magnetic separator which besides being simple and compact in construction, is also highly eiiicient in operation. The improved magnet construction and cooling system make it possible to create a magnetic field of exceptionally high intensity within the separating zone, thereby insuring maximum percentage of separation, and the improved formation of the magnets enables them to be compactly confined within limited space without undesirably obstructing the application of the cooling medium.

The invention is applicable to dry magnetic separators as well as to the wet separators specifically shown, and has proven highly satisfactory and successful in actual commercial use especially as applied to low grade iron ore.

It should be understood that it is not desired to limit the present invention to the exact de tails of construction and operation of the two types of wet magnetic separators herein specifically shown and described, for various modifications within the scope of the appended claims may occur to persons skilled in the art.

I claim:

1. In a magnetic separator, an endless carrier of non-magnetic material having outer and inner faces, means forming a separating zone adjacent to said carrier, means for moving said carrier to cause successive portions of said outer face to constantly advance through said zone, a series of eleetro-magnets each having a strip wound energizing coil of increasing ampere turns cooperating with a magnetic pole of decreasing transverse cross-section approaching said zone and coacting with said inner carrier face, said windings and poles coacting to create a magnetic field of high intensity extending along and within said zone, a casing enclosing all of said coils, a pump for constantly circulating cooling oil through said casing in contact with the outermost turns of said coils, and means for cooling said oil while being circulated by said pump.

2. In a magnetic separator, a carrier of nonmagnetic material, means forming a separating zone adjacent to said carrier, means for moving said carrier to advance the same through said zone, a direct current magnet having a strip wound coil of increasing ampere turns approaching said zone and cooperating with a magnetic core of diminishing transverse area approaching said zone, said core having a pole shoe coacting with said carrier and said winding and pole cooperating to create a magnetic field of high intensity within the separating zone, and means for constantly circulating cool oil in contact with said coils.

3. In a magnetic separator, means forming a separating zone: for removing magnetic particles from a mixture of magnetic and non-magnetic material, a non-magnetic carrier movable through said zone, a series of direct current electromagnets each having a magnetic core of diminishing transverse area approaching said zone surrounded by an energizing coil having increasing ampere turns also approaching said zone, each of said coils being composed of a succession of windings separated by gaps extending away from the corresponding core and the adjacent electromagnets of said series being separated from each other by spaces in open communication with said gaps, and means for circulating cooling medium through said spaces and gaps.

4. In a magnetic separator, means forming a separating zone for removing magnetic particles from a mixture of magnetic and non-magnetic material, a non-magnetic carrier movable through said zone, and a direct current electromagnet having a magnetic core composed of successive sections of diminishing transverse area approaching said zone surrounded by an energizing coil composed of a similar number of successive sections having increasing ampere turns also approaching said zone, said core and coil cooperating to create a magnetic field of high intensity within said separating zone for attracting magnetic particles upon said carrier.

5. In a magnetic separator, means forming a separating zone for removing magnetic particles from a mixture of magnetic and non-magnetic material, a non-magnetic carrier movable through said zone, a direct current electromagnet having a magnetic core composed of successive sections of diminishing transverse area approaching said zone surrounded by an energizing coil composed of a similar number of successive sections having increasing ampere turns also approaching said zone, each of said coil sections having parallel gaps therein extending away from the adjacent core sections and said core and coil cooperating to create a magnetic field of high intensity within said separating zone, and means for constantly circulating cool oil around said coil and through said gaps.

6. In a magnetic separator, means forming a separating zone, means for conducting mixed magnetic and non-magnetic particles into said zone, and a series of direct current electromagnets each having a magnetic core composed of successive sections of diminishing transverse area approaching said zone surrounded by an energizing coil composed of a similar number of successive interconnected sections having increasing ampere turns also approaching said zone, the successive electromagnets having opposite polarity and said cores and coils cooperating to create a magnetic field of high intensity within said separating zone for removing the magnetic particles.

'7. In a magnetic separator, means forming a separating zone, a carrier of non-magnetic material movable through said zone, and at least one direct current electromagnet having a magnetic core composed of several interconnected successive sections having diminishing transverse area approaching said zone and each section having uniform transverse area throughout its length and an energizing coil composed of a similar number of successive interconnected sections having increasing ampere turns also approaching said zone, said core and coil cooperating to create a magnetic field of high intensity along said carrier within said separating zone.

8. In a magnetic separator, means forming a separating zone, a carrier movable through said zone, a series of direct current electromagnets each having a magnetic core of diminishing transverse area approaching said zone surrounded by and cooperating with an energizing coil having increasing ampere turns also approaching said zone to create a magnetic field along said carrier, each of said coils being composed of a succession of windings having identical external dimensions separated by gaps extending away from the adjacent core and the adjacent electromagnets of said series being separated by spaces in open communication with said gaps, and means for constantly circulating precooled oil through said gaps and said spaces.

9. In a magnetic separator, means forming a separating zone, a carrier movable through said zone, a series of direct current electromagnets each having a magnetic core of diminishing transverse area approaching said zone surrounded by and cooperating with an energizing'coil having increasing ampere turns also approaching said zone to create a magnetic field along said carrier, each of said coils being composed of a succession of windings having identical external dimensions separated by gaps extending away from the adjacent core and the adjacent electromagnets of said series being separated by spaces in open communication with said gaps, a sealed casing enclosing all of said electromagnets, and means for constantly circulating pre-cooled oil at high velocity through said casing and said spaces and gaps.

10. In a magnetic separator, means forming a separating zone, a carrier forming an enclosure and being movable through said zone, a series of direct current electromagnets confined within the carrier and each having a magnetic core of diminishing transverse area approaching said zone surrounded by and cooperating with an energizing coil having increasing ampere turns also approaching said zone to create a magnetic field along said carrier, each of said coils being composed of a succession of windings having identical external dimensions separated by gaps extending away from the adjacent core and the adjacent electromagnets of said series being separated by spaces in open communication with said gaps, and means for constantly circulating precooled oil at high velocity through the interior of said carrier and said spaces and gaps;

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 440,424 Freeman Nov. 11, 1890 611,601 Bergmann Oct. 4, 1898 664,442 Sprang Dec. 25, 1900 1,048,824 De Nise et a1 Dec. 31, 1912 2,410,601 Crockett Nov. 5, 1946 2,471,911 Stearns May 31, 1949 2,479,373 Knotts Aug. 16, 1949 

